Castings, Casting Cores, and Methods

ABSTRACT

The pattern has a pattern material and a casting core combination. The pattern material has an airfoil. The casting core combination is at least partially embedded in the pattern material. The casting core combination comprises a metallic casting core and at least one additional casting core. The metallic casting core has opposite first and second faces. The metallic core and at least one additional casting core extend spanwise into the airfoil of the pattern material. In at least a portion of the pattern material outside the airfoil of the pattern material, the metallic casting core is bent transverse to the spanwise direction so as to at least partially surround an adjacent portion of the at least one additional casting core.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of Ser. No. 12/275,777, filed Nov. 21,2008, and entitled “Castings, Casting Cores, and Methods”, thedisclosure of which is incorporated by reference herein in its entiretyas if set forth at length.

BACKGROUND

The disclosure relates to investment casting. More particularly, itrelates to the investment casting of superalloy turbine enginecomponents.

Investment casting is a commonly used technique for forming metalliccomponents having complex geometries, especially hollow components, andis used in the fabrication of superalloy gas turbine engine components.The disclosure is described in respect to the production of particularsuperalloy castings, however it is understood that the disclosure is notso limited.

Gas turbine engines are widely used in aircraft propulsion, electricpower generation, and ship propulsion. In gas turbine engineapplications, efficiency is a prime objective. Improved gas turbineengine efficiency can be obtained by operating at higher temperatures,however current operating temperatures in the turbine section exceed themelting points of the superalloy materials used in turbine components.Consequently, it is a general practice to provide air cooling. Coolingis provided by flowing relatively cool air from the compressor sectionof the engine through passages in the turbine components to be cooled.Such cooling comes with an associated cost in engine efficiency.Consequently, there is a strong desire to provide enhanced specificcooling, maximizing the amount of cooling benefit obtained from a givenamount of cooling air. This may be obtained by the use of fine,precisely located, cooling passageway sections.

The cooling passageway sections may be cast over casting cores. Ceramiccasting cores may be formed by molding a mixture of ceramic powder andbinder material by injecting the mixture into hardened steel dies. Afterremoval from the dies, the green cores are thermally post-processed toremove the binder and fired to sinter the ceramic powder together. Thetrend toward finer cooling features has taxed core manufacturingtechniques. The fine features may be difficult to manufacture and/or,once manufactured, may prove fragile. Commonly-assigned U.S. Pat. Nos.6,637,500 of Shah et al., 6,929,054 of Beals et al., 7,014,424 of Cunhaet al., 7,134,475 of Snyder et al., and U.S. Patent Publication No.20060239819 of Albert et al. (the disclosures of which are incorporatedby reference herein as if set forth at length) disclose use of ceramicand refractory metal core combinations.

SUMMARY

One aspect of the disclosure involves a pattern for casting a componenthaving an airfoil. The pattern comprises a pattern material and acasting core combination. The pattern material has an airfoil. Thecasting core combination is at least partially embedded in the patternmaterial. The casting core combination comprises a metallic casting coreand at least one additional casting core. The metallic casting core hasopposite first and second faces. The metallic core and at least oneadditional casting core extend spanwise into the airfoil of the patternmaterial. In at least a portion of the pattern material outside theairfoil of the pattern material, the metallic casting core is benttransverse to the spanwise direction so as to at least partiallysurround an adjacent portion of the at least one additional castingcore.

In various implementations, the at least one additional casting core maycomprise at least one ceramic feedcore. A trunk of the ceramic feedcoremay form the adjacent portion. The component may be a blade wherein thepattern material has a fir-tree root portion and the adjacent portionextends at least partially within the root portion of the patternmaterial. There may be first and second said metallic cores combining tosurround at least 300° of the adjacent portion.

Other aspects of the disclosure involve methods for forming the patternand/or methods for casting using the pattern.

Other aspects of the disclosure involve gas turbine engine componentswhich may be cast from a shell formed from the pattern.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a cast blade.

FIG. 2 is a sectional view of the blade of FIG. 1, taken along line 2-2.

FIG. 3 is a sectional view of the blade of FIG. 1, taken along line 3-3.

FIG. 4 is a root ID view of the blade of FIG. 1.

FIG. 5 is a view of a pattern for forming the blade of FIG. 1 with acore assembly shown in solid line and pattern wax shown in brokenoutline.

FIG. 6 is a root ID view of the pattern of FIG. 5.

FIG. 7 is a suction side view of a second core assembly.

FIG. 8 is a pressure side view of the assembly of FIG. 7.

FIG. 9 is a view of the assembly of FIG. 8 with a pressure side RMCremoved.

FIG. 10 is a root ID view of an alternate blade.

FIG. 11 is a root ID view of a pattern for forming the blade of FIG. 10.

FIG. 12 is a view of a cast vane.

FIG. 13 is a flowchart of a manufacturing process.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows a gas turbine engine blade 20. The blade 20 has an airfoil22 extending from an inboard end 24 at the outboard surface of aninboard (inner diameter or ID) platform 26 to an outboard end or tip 28.The airfoil has a leading edge 30 and a trailing edge 32. The airfoilhas a suction side/surface 34 and a pressure side/surface 36 extendingbetween the leading edge 30 and the trailing edge 32. A convolutedattachment root (a so-called “fir-tree” root) 40 depends from anunderside (or inboard surface) of the platform 26 and has an inboardend/surface 42.

The exemplary blade 20 is cast from an alloy (e.g., a nickel-basedsuperalloy) and has an internal cooling passageway system. The exemplarycooling passageway system has a plurality of inlets. The exemplaryinlets are along the root 40, more particularly along the inboardend/surface 42. The exemplary blade has inlets 50A-50C, 52A-52C, and54A-54C (FIG. 4), discussed further below. The exemplary coolingpassageway system has a plurality of outlets. The exemplary outlets arealong the airfoil 22. The exemplary outlets include outlets 56A and 56B(FIG. 1) along the tip and outlets along the airfoil perimeter.Exemplary outlets along the airfoil perimeter include leading edgeoutlets 58 and trailing edge outlets 60 (FIG. 2). The exemplary trailingedge outlets 60 are formed by a trailing edge discharge slot 62.

The exemplary inlets 50A-50C, 52A-52C, and 54A-54C of FIG. 4 each feed arespective trunk 70A-70C, 72A-72C, and 74A-74C extending radiallyoutward within the root. In the exemplary airfoil, the trunks 70A-70Cmay each feed one or more spanwise feed passageways within and/orthrough the airfoil. Each spanwise feed passageway may have one or morespanwise legs (e.g., combinations of up-pass legs toward the tip anddown-pass legs back toward the root).

The exemplary trunks 72A-72C, however, merge near the platform to definea common spanwise passageway 92 (FIGS. 2&3). Similarly, the exemplarytrunks 54A-54C merge to form a common spanwise passageway 94. Theexemplary passageways 92 and 94 respectively extend to the tip outlets56A and 56B. The exemplary passageways 92 and 94 respectively extendadjacent the suction side/surface 34 and pressure side/surface 36.

The exemplary trunks 70A and 70B merge near the platform to define acommon spanwise feed passageway 96 (FIG. 2). The exemplary feedpassageway 96 extends to a terminal end recessed from the airfoil tip. Aleading edge impingement passageway 98 is fed from the passageway 96 viaimpingement holes 100. The exemplary trunk 70C continues to form aspanwise feed passageway 102 which, in turn, feeds the discharge slot62.

FIG. 4 shows each of the inlets 52A-52C and 54A-54C and associatedtrunks 72A-72C and 74A-74C as curving partially around the associatedinlet 50A-50C and trunk 70A-70C. Relative to the associated trunk70A-70C, each of the trunks 72A-72C and 74A-74C has an inboard surface130 and an outboard surface 132 and extends between lateral edges 134and 136 (shown, for example, for the trunk 74A). Between the edges 134and 136, the trunk 74A may have a net bend or change in angle (i.e.,distinguished from a trunk where the surfaces 130 and 132 are purelyplanar). An exemplary bend 138 (or bending region) is labeled in FIG. 4.

FIGS. 5 and 6 show a pattern 140 for casting the blade 20. The exemplarypattern comprises a combination 142 of casting cores (core combination)and a pattern material 144 in which the core combination is at leastpartially embedded. The pattern material has an external surfacegenerally corresponding to the external surface of the blade 20 (i.e.,having an airfoil 146, a platform 148, and a root 150). The corecombination 142 has an external surface (complementary to the matinginternal surface of the pattern material) generally corresponding toportions of the passageway system. For purposes of illustration, FIG. 5shows the combination 142 in solid lines and the pattern material 144 inbroken lines.

The exemplary core combination 142 is formed as the assembly of one ormore ceramic cores 160 and one or more metallic cores 162, 164. In theexemplary core combination 142, the metallic casting cores 162, 164 arerefractory metal cores (RMCs). Exemplary RMCs are refractory metal based(i.e., having substrates of at least fifty weight percent one or morerefractory metals such as molybdenum, tungsten, niobium, or the like,optionally coated). In the exemplary configuration, the RMC 162 isgenerally to the suction side of the pattern whereas the RMC 164 isgenerally to the pressure side.

In the exemplary core combination 142, the one or more ceramic cores 160include respective trunk portions 170A, 170B, and 170C for casting therespective trunks, 70A-70C. The RMC 162 includes trunk portions 172A,172B, and 172C for respectively casting the trunks 72A-72C. The RMC 164similarly includes trunk portions 174A, 174B, and 174C for respectivelycasting the trunks 74A-74C. Each of the exemplary trunk portions172A-172C and 174A-174C has an inboard surface 180, an outboard surface182, and lateral edges 184 and 186, respectively for casting thesurfaces 130 and 132 and edges 134 and 136 of the associated trunk. Oneor more of the trunk portions 172A-172C and 174A-174C may have one ormore bends 190 for forming the trunk bends 138 discussed above. In theexemplary core assembly (and associated casting) the leading andintermediate trunks 172A/174A and 172B/174B each have two such bends138: a leading bend and a trailing bend. The trailing such trunk172C/174C has only a single leading bend. The exemplary bends areadjacent associated corners of the cross-section of the trunk portions170A-170C. Corresponding features are thus formed in the casting. Therespective bends extend around local directions 802 of the respectivetrunk portions 170A-170C which is approximately coincident with aspanwise axial direction of the airfoil and a radial direction relativeto the installed condition on an engine. Exemplary bends are at least45° about this direction 802, more narrowly, at least 80° and, morenarrowly, 150-200°.

Steps in the manufacture 900 of the core assembly and casting arebroadly identified in the flowchart of FIG. 13. In a cutting operation902 (e.g., laser cutting, electro-discharge machining (EDM), liquid jetmachining, or stamping), one or more cuttings are cut from a blank forforming the RMCs. The exemplary blank is of a refractory metal-basedsheet stock (e.g., molybdenum or niobium) having a thickness in thevicinity of 0.01-0.10 inch (0.2-2.5 mm) between parallel first andsecond faces and transverse dimensions much greater than that. Eachexemplary cutting has the cut features of the associated RMC includingthe separations between the trunk portions and any holes (e.g., forforming posts or other features in the metallic core).

In a second step 904, if appropriate, each cutting is bent to form theassociated bends 190 as well as any other contouring (e.g., to moreslightly bend a portion of the metallic core to more closely follow theassociated pressure side or suction side of the airfoil). More complexforming procedures are also possible.

The RMC may be coated 906 with a protective coating. Exemplary coatingmaterials include silica, alumina, zirconia, chromia, mullite andhafnia. Coatings may be applied by any appropriate line-of sight ornon-line-of sight technique (e.g., chemical or physical vapor deposition(CVD, PVD) methods, plasma spray methods, electrophoresis, and sol gelmethods). Individual layers may typically be 0.1 to 1 mil (2.5 to 25micrometer) thick. Layers of Pt, other noble metals, Cr, Si, W, and/orAl, or other non-metallic materials may be applied to the metallic coreelements for oxidation protection in combination with a ceramic coatingfor protection from molten metal erosion and dissolution.

The RMCs may then be mated/assembled 908 to the feedcore. For example,the feedcore may be pre-molded 910 and, optionally, pre-fired.Optionally, a ceramic adhesive or other securing means may be used. Anexemplary ceramic adhesive is a colloid which may be dried by amicrowave process. Alternatively, the feedcore may be overmolded to theRMCs. For example, the RMCs may be placed in a die and the feedcore(e.g., silica-, zircon-, or alumina-based) molded thereover. Anexemplary overmolding is a freeze casting process. Although aconventional molding of a green ceramic followed by a de-bind/fireprocess may be used, the freeze casting process may have advantagesregarding limiting degradation of the RMCs and limiting ceramic coreshrinkage. By locating the mating joint/junction (not shown) between theRMCs and feedcore outside the subsequently overmolded pattern material(and thus outside the final casting) the distinct/separate inlets of theassociated feed passageway trunks may be created. Additionally, thechances for forming crystalline irregularities in the casting arereduced (e.g., if a single crystal casting is intended to be cast, anembedded joint may generate growth of distinct local crystals).

FIG. 13 also shows an exemplary method 920 for investment casting usingthe composite core assembly. Other methods are possible, including avariety of prior art methods and yet-developed methods. The coreassembly is then overmolded 930 with an easily sacrificed material suchas a natural or synthetic wax (e.g., via placing the assembly in a moldand molding the wax around it). There may be multiple such assembliesinvolved in a given mold.

The overmolded core assembly (or group of assemblies) forms a castingpattern with an exterior shape largely corresponding to the exteriorshape of the part to be cast. The pattern may then be assembled 932 to ashelling fixture (e.g., via wax welding between end plates of thefixture). The pattern may then be shelled 934 (e.g., via one or morestages of slurry dipping, slurry spraying, or the like). After the shellis built up, it may be dried 936. The drying provides the shell with atleast sufficient strength or other physical integrity properties topermit subsequent processing. For example, the shell containing theinvested core assembly may be disassembled 938 fully or partially fromthe shelling fixture and then transferred 940 to a dewaxer (e.g., asteam autoclave). In the dewaxer, a steam dewax process 942 removes amajor portion of the wax leaving the core assembly secured within theshell. The shell and core assembly will largely form the ultimate mold.However, the dewax process typically leaves a wax or byproducthydrocarbon residue on the shell interior and core assembly.

After the dewax, the shell is transferred 944 to a furnace (e.g.,containing air or other oxidizing atmosphere) in which it is heated 946to strengthen the shell and remove any remaining wax residue (e.g., byvaporization) and/or converting hydrocarbon residue to carbon. Oxygen inthe atmosphere reacts with the carbon to form carbon dioxide. Removal ofthe carbon is advantageous to reduce or eliminate the formation ofdetrimental carbides in the metal casting. Removing carbon offers theadditional advantage of reducing the potential for clogging the vacuumpumps used in subsequent stages of operation.

The mold may be removed from the atmospheric furnace, allowed to cool,and inspected 948. The mold may be seeded 950 by placing a metallic seedin the mold to establish the ultimate crystal structure of adirectionally solidified (DS) casting or a single-crystal (SX) casting.Nevertheless the present teachings may be applied to other DS and SXcasting techniques (e.g., wherein the shell geometry defines a grainselector) or to casting of other microstructures. The mold may betransferred 952 to a casting furnace (e.g., placed atop a chill plate inthe furnace). The casting furnace may be pumped down to vacuum 954 orcharged with a non-oxidizing atmosphere (e.g., inert gas) to preventoxidation of the casting alloy. The casting furnace is heated 956 topreheat the mold. This preheating serves two purposes: to further hardenand strengthen the shell; and to preheat the shell for the introductionof molten alloy to prevent thermal shock and premature solidification ofthe alloy.

After preheating and while still under vacuum conditions, the moltenalloy is poured 958 into the mold and the mold is allowed to cool tosolidify 960 the alloy (e.g., after withdrawal from the furnace hotzone). After solidification, the vacuum may be broken 962 and thechilled mold removed 964 from the casting furnace. The shell may beremoved in a deshelling process 966 (e.g., mechanical breaking of theshell).

The core assembly is removed in a decoring process 968 to leave a castarticle (e.g., a metallic precursor of the ultimate part). The castarticle may be machined 970, chemically and/or thermally treated 972 andcoated 974 to form the ultimate part. Some or all of any machining orchemical or thermal treatment may be performed before the decoring.

Provision of the bends 138 may reduce local thermal/mechanical stressconcentrations in the casting. For example, the root is subject to acombination of stresses from differential heating (e.g., hot gas flowingalong the airfoil contrasted with cool air flowing into the root) andmechanical loading (engagement forces between the root and disk, bothstatic and dynamic). The mechanical engagement forces, in particular,must pass around the trunks 54A-54C. Additionally, the thermal stressesmay be high near the corners of the trunk cross-sections. Accordingly,by shifting the edges 134, 136 away from the corners of thecross-sections of the trunks 50A-50C, the stress exacerbation caused bythe edges is reduced. For example, the bent RMCs of FIG. 4 may becontrasted with flat RMCs. For example, FIG. 6 shows the leading lateraledges 184 and trailing lateral edges 186 of the RMC trunks. For the RMCtrunks 172C and 174C, the trailing lateral portions are unbent, only theleading portions being bent. The trailing lateral edges are recessedupstream/forward of the adjacent ceramic feedcore trunk to avoid thestress fields associated with the trailing extremity of the associatedpassageway trunks 70C. If the leading lateral edges of the RMCs 172C and174C were similarly retracted/recessed (leaving only a flat narrowtrunk) such trunks would have little cross-sectional area and flowcapacity. If such flat RMCs were widened, extending the edge portionsinto the stress fields, thermal-mechanical damage could occur (e.g.,especially with high centrifugal loading on the blade root at highengine speed). Such centrifugal loading is not present in vanes.Accordingly, greater flexibility may be had in RMC positioning in vanes.For example, copending application (Attorney Docket 0007294-US(08-299))entitled CASTINGS, CASTING CORES, AND METHODS and filed on even dateherewith, disclosure of which is incorporated by reference as if setforth at length, discloses a number of vane embodiments having flat RMCtrunks with such relative RMC trunk and ceramic feedcore trunkpositioning and dimensioning.

FIGS. 7-9 show an alternate core assembly 400 comprising a ceramicfeedcore 402, a suction side feedcore 404, and a pressure side feedcore406.

Yet other wrapping configurations are possible.

FIGS. 10 and 11 respectively show a cast blade 500 and an associatedpattern 502. The pattern may have a ceramic core and the casting mayhave passageways cast by that ceramic core which are similar to the coreand passageways of FIGS. 6 and 4, respectively. The RMCs, may however,be differently wrapped. For example, FIG. 11 shows trunk portions 510A,510B, and 510C of a first RMC and trunk portions 512A, 512B, and 512C ofa second RMC. The exemplary trunk portion 510A generally wraps aroundboth leading pressure and suction side corners of the leading trunk ofthe ceramic feedcore while the trunk portion 512A generally wraps aroundthe trailing corners. This arrangement yet further shifts the edges 520of the associated passageways out of the high stress regions. Theexemplary embodiment also shows apertures 522 in various of the trunkportions of the RMCs. These apertures 522 cast associated posts 524extending through the associated trunk passageways to better supportmaterial surrounding the trunks cast by the ceramic feedcore.

FIG. 12 shows a vane 600 which may be cast by similar processes to thoseidentified above. The vane has an airfoil 602 extending between an IDplatform 604 and an OD shroud 606.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, theprinciples may be implemented using modifications of various existing oryet-developed processes, apparatus, or resulting cast article structures(e.g., in a reengineering of a baseline cast article to modify coolingpassageway configuration). In any such implementation, details of thebaseline process, apparatus, or article may influence details of theparticular implementation. Accordingly, other embodiments are within thescope of the following claims.

1. A gas turbine engine component comprising: an airfoil having: aleading edge; a trailing edge; a pressure side extending between theleading edge and trailing edge; a suction side extending between theleading edge and trailing edge; and one or more cooling passagewaysextending through the airfoil and comprising a trunk extending from aninlet, wherein: at said inlet, said trunk is at least partiallysurrounded by an additional passageway, said additional passagewayhaving a concavity with a spanwise axis of curvature.
 2. The componentof claim 1 wherein: the component is a blade and the port is in an IDface of a fir-tree root of the blade.
 3. The component of claim 1wherein: there are a first said additional passageway and a second saidadditional passageway cooperating to surround at least 300° of saidtrunk at said inlet.
 4. The component of claim 1 wherein: in transversesection, the at least one additional passageway bends by 150-200°. 5.The component of claim 1 wherein: in transverse section, the at leastone additional passageway bends by at least 45°.